This is an exercise that belongs in some homework section of the forums. From a mental ray diagram, I think the image is upright, shrunken and is a virtual image on the same side of the lens as the object.

It is really quite simple. Use the lens equation:

[tex] \frac{1}{s_0} + \frac{1}{s_i} = \frac{1}{f} [/tex]

The only things you must be careful about are the signs (+,-) of your quantities. Do we count a concave lens as negative or positive? Look that up in your notes (and read about the lens equation).

This is an exercise that belongs in some homework section of the forums. From a mental ray diagram, I think the image is upright, shrunken and is a virtual image on the same side of the lens as the object.

It is really quite simple. Use the lens equation:

[tex] \frac{1}{s_0} + \frac{1}{s_i} = \frac{1}{f} [/tex]

The only things you must be careful about are the signs (+,-) of your quantities. Do we count a concave lens as negative or positive? Look that up in your notes (and read about the lens equation).

thanks for your help,the equation you have given is the same as this one:
1/f = 1/u + 1/v

is that correct?? i dont know if the concave lens is positive or negative,it doesnt say in the question??

is that correct?? i dont know if the concave lens is positive or negative,it doesnt say in the question??

I`ve always used some thing calle da sign convention (there are diffrent ones but they all give the same answers!)

For the "real is positive" convention:

both f and R are positive for concave mirrors/lenses (real focus)
both f and R are negative for convex mirrors/lenses (virtual focus)
u is positive for real objects and negative for virtual objects
v is positive for real images and negative for virtual images

this becomes very important when you start putting more than one lense in a system!

I`ve always used some thing calle da sign convention (there are diffrent ones but they all give the same answers!)

For the "real is positive" convention:

both f and R are positive for concave mirrors/lenses (real focus)
both f and R are negative for convex mirrors/lenses (virtual focus)
u is positive for real objects and negative for virtual objects
v is positive for real images and negative for virtual images

this becomes very important when you start putting more than one lense in a system!

Whats "R"???...oh so if i had the same question but the lens was convex then i would use the same equation as before but the focal length would be negative??

Maybe the language I used confused you, sorry
If the object is 24 cm away from the lense and the image formed is 72cam away then, the magnification is the relationship between the two distances,
[tex] - \frac {72}{24} = -3 [/tex]

Maybe the language I used confused you, sorry
If the object is 24 cm away from the lense and the image formed is 72cam away then, the magnification is the relationship between the two distances,
[tex] - \frac {72}{24} = -3 [/tex]

Ok first I must readdress an errror I made! I gave you the wrong sign convention! Ooops

So ... for the Real is positive convention ;

f is positive for a convex lense (real focus)
f is negative for a concave lense (virtual focus)
u is positive for real objects and negative for virtual objects
v is positive for real images and negative for virtual images

Ok first I must readdress an errror I made! I gave you the wrong sign convention! Ooops

So ... for the Real is positive convention ;

f is positive for a convex lense (real focus)
f is negative for a concave lense (virtual focus)
u is positive for real objects and negative for virtual objects
v is positive for real images and negative for virtual images

keep practising it will become natural soon as you`ve allready got a good understanding of optics!

A my idol once said " Optics are either very easy or very hard" - Richard Feynman

Thanks,that all great..the only problem i have is when i try to use that equation i cant get -72??..i keep gettin 1/72 or -7/72???..how do you end up with just -72??...and finally when i do my ray diagram it should look like the one you have attatched except that my lengths will be different,is that right??

i keep gettin 1/72 or -7/72???..how do you end up with just -72??...and finally when i do my ray diagram it should look like the one you have attatched except that my lengths will be different,is that right??

Thanks,that all great..the only problem i have is when i try to use that equation i cant get -72??..i keep gettin 1/72 or -7/72???..how do you end up with just -72??...and finally when i do my ray diagram it should look like the one you have attatched except that my lengths will be different,is that right??

as long as the drawing is in proportion it will be fine. The one i've done is to scale, 1:10, the focus I've placed on the opposite side to the object to remind me it`s 'negative' (from the sign convention) and the image is on the same side showing that it is virtual

as long as the drawing is in proportion it will be fine. The one i've done is to scale, 1:10, the focus I've placed on the opposite side to the object to remind me it`s 'negative' (from the sign convention) and the image is on the same side showing that it is virtual

thanks,i think ive got the understanding of that now and should be able to do a similar question if it was on a convex lens...can i ask you another question??its a pretty long question and i dont know how to tackle it??